1. Field of the Invention
The present invention relates to an asphalt composition. More particularly, the present invention is concerned with an asphalt composition comprising a block copolymer component (I), an asphalt (II) and at least one vulcanizing agent (III) selected from the group consisting of sulfur and a sulfur-containing compound, wherein the block copolymer component (I) comprises at least one modified block copolymer comprising a base block copolymer comprising at least one vinyl aromatic polymer block (A) and at least one conjugated diene polymer block (B), and a functional group-containing modifier group bonded to the base block copolymer. The asphalt composition of the present invention is advantageous not only in that it has a high softening point and excellent properties with respect to ductility, storage stability at high temperatures and flexural properties at low temperatures, but also in that, when the asphalt composition is used in road paving, there can be formed a pavement layer having excellent dynamic stability and excellent aggregate-gripping properties. Therefore, the asphalt composition of the present invention is very suitable for use in road paving. Thus, the asphalt composition of the present invention can be advantageously used as a binder for road paving, especially as a binder for forming a drainage pavement.
2. Prior Art
Conventionally, an asphalt composition has been used in a wide variety of fields, such as the fields of a material for use in road paving, a material for a waterproof sheet, a material for a sound insulating sheet and a roofing material. In these fields, a number of attempts have been made to improve the properties of the asphalt composition by adding various polymers to the asphalt composition. As examples of such polymers, there can be mentioned an ethylene/vinyl acetate copolymer, an ethylene/ethyl acrylate copolymer, a rubber latex, and a block copolymer comprising conjugated diene monomer units and vinyl aromatic hydrocarbon monomer units.
However, in recent years, due to the expansion of traffic and the increase in the number of expressways, there is a growing demand for an asphalt mixture (which is comprised of a plurality of aggregates and an asphalt composition as a binder) having excellent strength and excellent abrasion resistance. Further, there is a growing demand for an asphalt mixture which not only has excellent strength and excellent abrasion resistance, but also can be used to form a highly open graded pavement layer which can improve the drainage properties and noise reduction properties of expressways. For achieving the above-mentioned excellent properties, the asphalt composition is required to have a high softening point and high mechanical strengths (such as high flexural stress and excellent aggregate-gripping properties). For meeting this requirement, it has been attempted, for example, to employ a method in which a block copolymer having a high molecular weight is incorporated into the asphalt composition. However, such method is disadvantageous in that the resultant asphalt composition containing a high molecular weight block copolymer incorporated therein has unsatisfactory storage stability at high temperatures and, hence, its melt viscosity becomes increased under high temperature conditions, thus rendering poor the workability of the asphalt composition during the road paving.
For improving the storage stability of an asphalt composition at high temperatures, it has generally been attempted to add an aromatic process oil to the asphalt composition, or effect a crosslinking of the asphalt composition by the use of sulfur or a peroxide. For example, Examined Japanese Patent Application Publication No. Sho 57-24385 (corresponding to U.S. Pat. No. 4,145,322) discloses a crosslinking using sulfur. On the other hand, Examined Japanese Patent Application Publication No. Hei 1-13743 (corresponding to U.S. Pat. Nos. 4,554,313 and 4,567,222) discloses a crosslinking using a polysulfide having a specific structure. Further, Unexamined Japanese Patent Application Laid-Open Specification No. Hei 3-501035 (corresponding to U.S. Pat. No. 5,508,112) discloses a crosslinking using a combination of sulfur as a vulcanizing agent and a sulfur-containing compound as a vulcanization accelerator. However, any of the above-mentioned techniques is still unsatisfactory in improving the storage stability of an asphalt composition at high temperatures. Also, it has been desired to develop an asphalt composition which not only has excellent storage stability at high temperatures, but also can be used for forming a pavement layer having excellent dynamic stability and excellent aggregate-gripping properties.